As a shift worker of some seventeen years, I feel I’m qualified to advise here. The biggest issue is your brain. Stop thinking about it! That’ll sort it. Just honestly don’t worry about it and all will be well. You’ll either a) not wake up at 3am, o more likely, and this is the trick b) wake up at 3am but just shrug, turn over and be snoozing again immediately. The fact you even know it’s 3am means you are worrying too much about it, don’t look at that clock, and especially DON’T look at the phone!!! Just shrug and go back to sleep. My own sleep habits are proof that it doesn’t need to be dark, it doesn’t have to be quiet, you just have to be a bit tired, and not worried about it.